<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id="an">按钮</div>
</body>
<style>
    *{
        padding: 0;
        margin: 0;
    }
    body{
        background: #000;
    }
    #an {
        position: absolute;
        left: 50%;
        top: 50%;
        transform: translate(-50%, -50%);
        /* text-decoration: none; */
        font-size: 24px;
        background: linear-gradient(90deg, #03a9f4, #f441a5, #ffeb3b, #03a9f4);
        background-size: 400%;
        width: 400px;
        height: 100px;
        line-height: 100px;
        text-align: center;
        color: #fff;
        text-transform: uppercase;
        border-radius: 50px;
        z-index: 1;
    }

    #an::before{
        content: '';
        position: absolute;
        left: -5px;
        right: -5px;
        top: -5px;
        bottom: -5px;
        background: linear-gradient(90deg, #03a9f4, #f441a5, #ffeb3b, #03a9f4);
        background-size: 400%;
        border-radius: 50px;
        filter: blur(20px);
        z-index: 1;
    }

    #an:hover {
        animation: sun 8s infinite;
    }

    @keyframes sun {
        100% {
            background-position: -400% 0;
        }
    }
</style>

</html>